This application is for a Reading Center of a national collaborative randomized controlled clinical trial of photocoagulation treatment for central vein occlusion. The study will be conducted at 8 clinical centers with the Reading Center at the Bascom Palmer Eye Institute (University of Miami), and the Coordinating Center at Scott and White Hospital in Temple, Texas (Texas A&M University). Patients will be entered into four study groups: Non-perfused (Group N); Macular edema (Group M); Perfused (Group P); and indeterminant (Group I). Eyes in the first two groups will be randomly assigned to photocoagulation treatment and a control group. Patients in Groups P and I will be followed for natural history and for possible later entry into the randomized study. Estimated recruitment is 240 patients in Group N; 480 in Group P and 240 in Group I. Approximately 50% of these patients will also qualify for Group M. Patients will be recruited for the first 3 years of this 5 year study, and all patients will be followed until termination of the study. The study is designed to provide information regarding whether or not photocoagulation is efficacious in preventing iris neovascularization and subsequent neovascular glaucoma in eyes with central vein occlusion and retinal non-perfusion, and whether or not photocoagulation is useful in preserving visual acuity in eyes with central vein occlusion and macular edema. Information collected at base line and each follow-up visit will be forwarded to the Coordinating Center for processing and analysis. Photographs taken to record the appearance of the iris and retina, as well as fluoresein angiographic studies of the retina will be forwarded to the Reading Center for analysis and interpretation. The inclusion of patients in the various groups in the study will depend upon the interpretation of the fluoresein angiogram. The interpretation of iris photographs will determine the outcome variable, iris neovascularization. A Data and Safety Monitoring Committee will review interim results of the study every six months.